Methods for suppressing noise in volume data are known in principle. Thus, noise can be effectively reduced with the aid of linear low pass filtering. However, in this case, there is a reduction in the sharpness of the data material and thus in the quality of the imaging of small structures. This simple approach can therefore be used only in a limited way to improve the image material.
Another method is based on two- or three-dimensional, iterative filtering of the data material, information relating to the position and orientation of edges being input in each step. Reference may be made by way of example in this context to T. Chan, S. Osher, and J. Shen; The digital TV filter and non-linear denoising; http://citeseer.nj.nec.com/article/chan01digital.html, 1999, Tech. Report CAM 99-34, Department of Mathematics, UCLA, Los Angeles, Calif., 1999; IEEE Trans. Image Process., to appear [Call date May 15, 2003] or Winkler G., Hahn K., Aurich V.; Recent Developments in Edge-Preserving Smoothing; Institute of Biomathematics and Biometry, GSF-National Research Center for Environment and Health, Neuherberg, 1998.
Because of the “central limit” theorem, these above-named methods lead to a Gauss-type filter characteristic that for radiologists frequently does not correspond to the customary image impression of diagnostic images and is therefore rejected. A further problem resides in the run time of such algorithms which, because of many iterations, is in the range of minutes per axial section, and therefore renders the method clinically inappropriate.
Nevertheless, there is still a requirement to find a possibility of dose optimization so that the radiation load on patients owing to diagnostic methods can be kept as low as possible or reduced.